An aqueous inkjet ink and receiver combination wherein the aqueous inkjet ink comprises: a pigment; a polymer binder containing less than 25% of a hydrophilic monomer by weight of the total polymer; the binder being dispersible but insoluble in aqueous media; at least one surfactant; a humectant; and wherein the receiver comprises a non-absorbing substrate.

Claim:

What is claimed is:

1. An aqueous inkjet ink and receiver combination wherein said aqueous ink jet ink comprises: a pigment; a polymer binder containing less than 25% of hydrophilic monomer byweight of the total polymer, the binder being dispersible but insoluble in aqueous media; at least one surfactant; a humectant; and wherein said receiver comprises a non-absorbing substrate.

2. The combination of claim 1 wherein the weight ratio of the pigment to the polymer binder is 1:20 to 20:1.

3. The combination of claim 1 wherein the weight ratio of the pigment to the polymer binder is 1:5 to 2:1.

4. The combination of claim 1 wherein said pigment comprises up to 10% by weight of the ink composition.

5. The combination of claim 1 wherein the pigment comprises up to 5% by weight of the ink composition.

6. The combination of claim 1 wherein the pigment has an average particle size of less than 0.5 micron.

7. The combination of claim 1 wherein the surfactant is a siliconated or a fluorinated surfactant or a mixture of both.

8. The combination of claim 1 wherein the polymer binder is a polyester, an acrylic polymer or a polyurethane.

20. The combination of claim 1 wherein the polymer binder contains at least one reactive group capable of reacting with a cross-linking agent.

21. The combination of claim 20 wherein the reactive group is an amine, carboxylic, hydroxy, epoxy, urea, urethane, or an active carbonyl.

22. The combination of claim 21 wherein the reactive group is an active carbonyl and wherein said active carbonyl is aldehyde or keto.

23. The combination of claim 1 wherein the polymer binder has a Tg of -50 to 80.degree. C.

24. The combination of claim 1 wherein the polymer binder has an average particle size of less than 0.5 micron.

25. The combination of claim 6 wherein the polymer binder contains less than 10% of hydrophilic monomer by weight of the total polymer.

26. The combination of claim 1 wherein the polymer binder contains less than 5% of hydrophilic monomer by weight of the total polymer.

27. The combination of claim 1 wherein all monomer units in the polymer binder are hydrophobic.

28. The combination of claim 1 where the pigment is a self-dispersing pigment, an encapsulated pigment or a pigment dispersed by a dispersant.

29. The combination of claim 1 wherein the non-absorbing substrate is a plastic, glass, ceramic or metal substrate.

30. The combination of claim 29 wherein the plastic substrate is an untreated vinyl.

Description:

FIELD OF THE INVENTION

The present invention relates to an ink jet ink and receiver combination wherein the aqueous inkjet ink comprises a pigment and a polymer binder, and the receiver comprises a non-absorbing substrate, e.g., an untreated vinyl.

BACKGROUND OF THE INVENTION

Ink jet printing is a non-impact method for producing images by the deposition of ink droplets on a substrate (paper, transparent film, fabric, etc.) in response to digital signals. Ink jet printers have found broad applications across marketsranging from industrial labeling to short run printing to desktop document and pictorial imaging and large format printing for outdoor applications such as banners, signage, displays, posters, billboard and bus wraps.

This technique of printing is well suited for printing on a variety of surfaces (receivers) including porous and non-porous surfaces. Porous inkjet receivers have the advantage of large fluid intake and this provides fast printing speed. However, in some applications, such as banners, signage, displays, posters, billboard and bus wraps, these porous receivers suffer from durability issues such as lightfastness, waterfastness, abrasion resistance and weather resistance. In order toovercome these problems, the prints are usually post treated by methods such as lamination, which adds to the cost considerably. Historically, in order to overcome these problems, solvent based inks or UV curable inks were developed for printing onnon-absorbing substrates such as vinyl to achieve the desired durability. U.S. Pat. No. 4,106,027 describes such a solvent-based ink that is suitable for printing images on non-absorbing receivers with improved adhesion and durability. EP 0 882 104B1 describes a UV curable inkjet ink composition for better durability of the print on non-absorbing substrate. A significant environmental, health and safety concern with both of these types of ink is the evaporation of solvent or UV monomer duringprinting.

U.S. Pat. No. 6,087,416 describes the use of an aqueous based pigment ink for printing on non-absorbing vinyl substrate. That ink contains a grafted copolymer binder that is soluble in the aqueous vehicle but insoluble in water. However, theproblem with the ink is that, due to the soluble nature of the binder in the ink vehicle, the ink viscosity is high and the printing reliability is poor. In addition, the printed images are not durable to solvents.

U.S. Pat. No. 4,762,875 described a printing ink containing pigment and polymer additives for plastics and metal surfaces. However, there is a problem with this invention that the solid content for this ink is high, therefore the viscosity ofthe ink is too high for inkjet ink applications; in addition, the additives used in this invention is hydrophilic in nature therefore the resulted coatings has poor water resistance.

Therefore, there is a need for an aqueous based ink jet ink that provides good waterfastness, lightfastness, abrasion resistance, good adhesion to non-absorbing substrates including untreated vinyl, and that can be printed reliably through apiezo or thermal printhead.

SUMMARY OF THE INVENTION

The present invention provides an aqueous based ink jet ink that provides good waterfastness, lightfastness, abrasion resistance, good adhesion to non-absorbing substrates including untreated vinyl, and can be printed reliably through a piezo orthermal printhead. These and other objects are achieved in accordance with the present invention which comprises an ink jet ink and receiver combination wherein the ink comprises: a pigment; a polymer binder containing less than 25% of hydrophilicmonomer by weight of the total polymer, which is dispersible but insoluble in aqueous media, at least one surfactant; a humectant; and wherein the receiver comprises a non-absorbing substrate.

It was found that the colloid stability, stain resistance and abrasion resistance of an ink jet image was improved using the composition described herein.

DETAILED DESCRIPTION OF THE INVENTION

The ink composition of the present invention is suited for printing on a variety of substrates, including non-absorbing substrates. The non-absorbing substrates that may be used in the present invention include any substrate that is essentiallynon-porous. They are usually not specially treated for additional liquid absorption. Therefore, these materials have very low or no liquid absorbing capacity. Examples of such non-absorbing substrates are metals such as aluminum, copper, stainlesssteel and alloy etc.; plastics such as vinyl, polycarbonate, polytetrafluoroethylene (PTFE), polyethylene, polypropylene, polystyrene, cellulose; and other substrates such as ceramics, glass.

In order to achieve good image durability when printing aqueous based inks onto a non-absorbing substrate, the polymeric binder in the ink composition needs to be essentially hydrophobic, capable of providing good adhesion strength to thenon-absorbing substrate, and also not be easily re-dispersible in water after drying. In addition, good ink storage stability as well as nozzle jettability requires the hydrophobic polymer binder to be both sufficiently stable as a dispersion and becompatible with other ink components, such as surfactant, colorants and humectants. One way to achieve this is to design the polymer binder to be dispersible in an aqueous ink environment but not soluble in aqueous media. This achieves low inkviscosity, and the resulting printed images exhibit durability to both water and solvents. Furthermore, the ink should have sufficiently low surface tension to have good wettability when printing unto a non-absorbing substrate.

The pigment used in the current invention can be either self-dispersible such as those described in U.S. Pat. No. 5,630,868, encapsulated as those described in the pending U.S. patent application Ser. No. 09/822,723, filed Mar. 30, 2001, orcan be stabilized by a dispersant. The process of preparing inks from pigments commonly involves two steps: (a) a dispersing or milling step to break up the pigment to the primary particle, and (b) dilution step in which the dispersed pigmentconcentrate is diluted with a carrier and other addenda to a working strength ink. In the milling step, the pigment is usually suspended in a carrier (typically the same carrier as that in the finished ink) along with rigid, inert milling media. Mechanical energy is supplied to this pigment dispersion, and the collisions between the milling media and the pigment cause the pigment to deaggregate into its primary particles. A dispersant or stabilizer, or both, is commonly added to the pigmentdispersion to facilitate the deaggregation of the raw pigment, to maintain colloidal particle stability, and to retard particle reagglomeration and settling.

There are many different types of materials which may be used as milling media, such as glasses, ceramics, metals, and plastics. In a preferred embodiment, the grinding media can comprise particles, preferably substantially spherical in shape,e.g., beads, consisting essentially of a polymeric resin. In general, polymeric resins suitable for use as milling media are chemically and physically inert, substantially free of metals, solvent and monomers, and of sufficient hardness and firabilityto enable them to avoid being chipped or crushed during milling. Suitable polymeric resins include crosslinked polystyrenes, such as polystyrene crosslinked with divinylbenzene, styrene copolymers, polyacrylates such as poly(methyl methylacrylate),olycarbonates, polyacetals, such as Derlin.TM., vinyl chloride polymers and copolymers, polyurethanes, polyamides, poly(tetrafluoroethylenes), e.g., Teflon.TM., and other fluoropolymers, high density polyethylenes, polypropylenes, cellulose ethers andesters such as cellulose acetate, poly(hydroxyethylmethacrylate), poly(hydroxyethylacrylate), silicone containing polymers such as polysiloxanes and the like. The polymer can be biodegradable. Exemplary biodegradable polymers include poly(lactides),poly(glycolids) copolymers of lactides and glycolide, polyanhydrides, poly(imino carbonates), poly(N-acylhydroxyproline) esters, poly(N-palmitoyl hydroxyprolino) esters, ethylene-vinyl acetate copolymers, poly(orthoesters), poly(caprolactones), andpoly(phosphazenes). The polymeric resin can have a density from 0.9 to 3.0 g/cm3. Higher density resins are preferred inasmuch as it is believed that these provide more efficient particle size reduction. Most preferred are crosslinked or uncrosslinkedpolymeric media based on styrene.

Milling can take place in any suitable grinding mill. Suitable mills include an air jet mill, a roller mill, a ball mill, an attritor mill and a bead mill. A high speed mill is preferred. By high speed mill we mean milling devices capable ofaccelerating milling media to velocities greater than about 5 meters per second. Sufficient milling media velocity is achieved, for example, in Cowles-type saw tooth impeller having a diameter of 40 mm when operated at 9,000 rpm. The preferredproportions of the milling media, the pigment, the liquid dispersion medium and dispersant can vary within wide limits and depends, for example, up on the particular material selected and the size and density of the milling media etc. After milling iscomplete, the dispersion of active material is separated from the grinding media by simple sieving or filtration. With either of the above modes, the preferred amounts and ratios of the ingredients of the mill grind will vary widely depending upon thespecific materials and the intended applications. The contents of the milling mixture comprise the mill grind and the milling media. The mill grind comprises pigment, dispersant and a liquid carrier such as water. For aqueous ink jet inks, the pigmentis usually present in the mill grind at 1 to 50 weight %, excluding the milling media. The weight ratio of pigment to dispersant is 20:1 to 1:2. The high speed mill is a high agitation device, such as those manufactured by Morehouse-Cowles, Hockmeyeret al.

The dispersant is another ingredient in the mill grind. It can be either a small molecule or a polymer. Preferred dispersants used in the present invention include sodium dodecyl sulfate, acrylic and styrene-acrylic copolymers, such as thosedisclosed in U.S. Pat. Nos. 5,085,698 and 5,172,133, and sulfonated polyesters and styrenics, such as those disclosed in U.S. Pat. No. 4,597,794. Other patents referred to above in connection with pigment availability also disclose a wide varietyof dispersants. The dispersant used in the examples is potassium N-methyl-N-oleoyl taurate (K-OMT).

The milling time can vary widely and depends upon the pigment, mechanical means and residence conditions selected, the initial and desired final particle size, etc. For aqueous mill grinds using the preferred pigments, dispersants, and millingmedia described above, milling times will typically range from 1 to 100 hours. The milled pigment concentrate is preferably separated from the milling media by filtration.

The pigment particles useful in the invention may have any particle sizes which can be jetted through a print head. Preferably, the pigment particles have a mean particle size of less than about 0.5 micron, more preferably less than about 0.2micron.

In the case of organic pigments, the ink may contain up to approximately 20% pigment by weight, but will generally be in the range of approximately 0.1 to 10%, preferably approximately 0.1 to 5%, by weight of the total ink composition for mostink jet printing applications. If an inorganic pigment is selected, the ink will tend to contain higher weight percentages of pigment than with comparable inks employing organic pigments.

Instead of pigment, a dye can also be used in the current invention. Preferably, the dye is a water insoluble dye. To make the ink, the water insoluble dye can be dispersed or encapsulated into water dispersible particles as disclosed in U.S. Ser. No. 10/020,694, filed Dec. 14, 2001. A broad range of water-insoluble dyes may be used in the invention such as an oil dye, a disperse dye, or a solvent dye, such as Ciba-Geigy Orasol Red G, Ciba-Geigy Orasol Blue GN, Ciba-Geigy Orasol Pink, andCiba-Geigy Orasol Yellow. Preferred water-insoluble dyes can be xanthene dyes, methine dyes, polymethine dyes, anthroquinone dyes, merocyanine dyes, azamethine dyes, azine dyes, quinophihalone dyes, thiazine dyes, oxazine dyes, phthalocyanine dyes, monoor poly azo dyes, and metal complex dyes. More preferably, the water insoluble dyes can be an azo dye such as a water insoluble analog of the pyrazoleazoindole dye disclosed in U.S. Pat. No. 6,468,338, incorporated herein by reference, and thearylazoisothiazole dye disclosed in U.S. Pat. No. 4,698,651, incorporated herein by reference, or a metal-complex dye, such as the water-insoluble analogues of the dyes described in U.S. Pat. Nos. 5,997,622 and 6,001,161, both incorporated herein byreference, i.e., a transition metal complex of an 8-heterocyclylazo-5-hydroxyquinoline. The solubility of the water insoluble dye used in the present invention should be less than 1 g/L in water, and more preferably less than 0.5 g/L in water.

The water insoluble dye can be present in any effective amount in the ink of the present invention, usually up to about 20% by weight of an ink jet ink composition, and preferably from about 0.05 to 15 wt. %.

The polymers used in the current invention are essentially hydrophobic polymers of any composition that can be stabilized but not dissolved in water-based ink medium. They can be either polymer latex or water dispersible polymer. Suchhydrophobic polymers are generally classified as either condensation polymer or addition polymers. Condensation polymers include, for example, polyesters, polyamides, polyurethanes, polyureas, polyethers, polycarbonates, polyacid anhydrides, andpolymers comprising combinations of the above-mentioned types. Addition polymers are polymers formed from polymerization of vinyl-type monomers including, for example, allyl compounds, vinyl ethers, vinyl heterocyclic compounds, styrenes, olefins andhalogenated olefins, unsaturated acids and esters derived from them, unsaturated nitrites, vinyl alcohols, acrylamides and methacrylamides, vinyl ketones, multifunctional monomers, or copolymers formed from various combinations of these monomers. Mostof monomer units in the polymer used in the invention may be hydrophobic, and the content of the hydrophilic monomer is less than 25% by weight of the total polymer, more preferably less than 10% by weight of the total polymer, most preferably less than5% by weight of the total polymer.

In a preferred embodiment of the invention, the polymer latex or water dispersible polymer is a styrene/acrylic polymer, a polyester or a polyurethane.

The polymer can be prepared in aqueous media using well-known free radical emulsion polymerization methods and may consist of homopolymers made from one type of the above-mentioned monomers or copolymers made from more than one type of theabove-mentioned monomers. Polymers comprising monomers which form water-insoluble homopolymers are preferred, as are copolymers of such monomers. Preferred polymers may also comprise monomers which give water-soluble homopolymers, if the overallpolymer composition is sufficiently water-insoluble to form a latex. The polymer can be prepared by emulsion polymerization, solution polymerization, suspension polymerization, dispersion polymerization, ionic polymerization (cationic, anionic), AtomicTransfer Radical Polymerization, and other polymerization methods known in the art of polymerization.

The first class of preferred polymer include those styrene/acrylic polymers prepared by free-radical polymerization of vinyl monomers in aqueous emulsion. The polymer latex can be homopolymer or copolymer or cross-linked polymers comprisingethylenically-unsaturated hydrophobic monomers which form water-insoluble homopolymers are preferred, as are copolymers of such monomers, which may also comprise ethylenically-unsaturated hydrophilic monomers which give water-soluble homopolymers, if theoverall polymer composition is sufficiently water-insoluble to form a latex.

In a preferred embodiment of the invention, the ethylenically-unsaturated monomers are halogenated. Examples are vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, vinyl bromide and vinylidene bromide, chloromethacrylicacid and the like.

The second class of polymer used in the invention may be water dispersible polyesters. The water-dispersible polyester ionomer polymers used in this invention have the following general formula: ##STR1##

wherein: A is the residue of one or more diol components which together comprise 100 mole % of recurring units and is represented by the following structure:

Examples of water dispersible polyesters useful in the invention include Eastman AQ.RTM. polyesters, (Eastman Chemical Company). Eastman Polyesters AQ 29, AQ 38, and AQ 55 are composed of varying amounts of isophthalic acid, sodiumsulfoisophthalic acid, diethylene glycol, and 1,4-cyclohexanedimethanol. These thermoplastic, amorphous, ionic polyesters are prepared by a melt-phase condensation polymerization at high temperature and low pressure, and the molten product is extrudedinto small pellets. The solid polymer disperses readily in water at 70.degree. C. with minimal agitation to give translucent, low viscosity dispersions containing no added surfactants or solvents. Varying the amount of ionic monomers, i.e.,sulfoisophthalic acid, can control the particle size. The particle sizes range from 0.02 to 0.1 .mu.m.

The third class of polymer used in the invention may be an aqueous dispersible polyurethane. Useful polyurethanes are disclosed in U.S. Pat. No. 6,268,101, the disclosure of which is hereby incorporated by reference. These materials may beprepared as described in "Polyurethane Handbook," Hanser Publishers, Munich Vienna, 1985. Examples of aqueous dispersible polyurethanes are Witcobond.RTM. polyurethane dispersion such as W-240, W-232 and W-254 by Crompton Corp. or Sancure.RTM. polyurethane by BF Goodrich Company.

The polymer employed in the invention in general has a Tg of -50 to 150.degree. C., preferably 5 to 100.degree. C., most preferably 10 to 80.degree. C.

The polymer latex employed in the invention in general have an average particle size of less than 2 .mu.m, preferably less than 0.5 .mu.m, more preferably less than 0.25 .mu.m.

The polymer latex used in the invention is present in the ink jet ink generally from 0.1% to 20% by weight, preferably from 0.5% to 10% by weight.

The polymeric binder employed in the present invention preferably contains at least one reactive functional group that is capable of reacting with a crosslinking agent. Typical examples of such reactive groups are epoxy groups(preferablyglycidyl), hydroxyalkyl groups, amines, carboxyl groups, active carbonyls such as aldehyde or ketones, urea or urethane groups and alcohols.

Preferably, the ink employed in the combination of the invention further comprises a cross-linking agent that is capable of reacting with the polymer binder at elevated temperatures or other photo/chemical treatment. Typical cross-linking agentsfor carbonyl containing reactive groups are such as keto or aldehyde can be di- or polyamine such as melamine, di- or polyhydrazide, isophorone diamine, 4,7-dioxadecene-1,10-diamine, or derivatives of dibasic acids such as adipic dihydrazide, succinicdihydrazide, phthalica acid dihydrazide, dialkylmine derivatives of polyalkyl glycols, alkyl di- or triamines. Typical crosslinking agent for reactive groups such as hydroxyl are polyisocyanates, melamine and glycoluril.

Polymer dispersions containing cross-linking agent can also be used. For examples, they can be commercially available such as self-cross-linkable polyurethane W-240 and W-254 from Crompton Corp., and Acronal D6079, Acronal A603 from BASF andEsicryl 100XL from Cook Composites & Polymers.

The amount of aqueous carrier medium is in the range of approximately 70 to 99 weight %, preferably approximately 90 to 98 weight %, based on the total weight of the ink. A mixture of water and a polyhydric alcohol, such as diethylene glycol, isuseful as the aqueous carrier medium. In a preferred embodiment, the inks contain from about 5 to about 60 weight % of water miscible organic solvent based on the total weight of the aqueous carrier medium.

Jet velocity, separation length of the droplets, drop size and stream stability are greatly affected by the surface tension and the viscosity of the ink. The ink jet inks suitable for use with ink jet printing systems and to apply tonon-absorbing substrates, especially high surface energy hydrophobic surfaces, should have a surface tension in the range of about 20 dynes/cm to about 60 dynes/cm and, more preferably, in the range 20 dynes/cm to about 35 dynes/cm. Control of surfacetensions in aqueous inks is accomplished by additions of small amounts of surfactants. The level of surfactants to be used can be determined through simple trial and error experiments, usually about 0.1% to about 6%, preferably, 0.5% to about 4% byweight of the total ink composition. Anionic, cationic and nonionic surfactants may be selected from those disclosed in U.S. Pat. Nos. 5,324,349; 4,156,616 and 5,279,654 as well as many other surfactants known in the ink jet ink art. Commercialsurfactants include the Surfynols.RTM. from Air Products; the Zonyls.RTM. from DuPont and the Fluorads.RTM. from 3M. Preferred surfactants can be silicon surfactants or fluorinated surfactants. Preferred silicon surfactants are available fromBYK-Chemie as BYK surfactants, and from Crompton Corp, as Silwet.RTM. surfactants. Commercially available fluorinated surfactants can be the Zonyls.RTM. from DuPont and the Fluorads.RTM. from 3M, they can be used alone or in combination with othersurfactants.

A humectant is added to the composition employed in the process of the invention to help prevent the ink from drying out or crusting in the orifices of the ink jet printhead. Polyhydric alcohols useful in the composition employed in theinvention for this purpose include, for example, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, 2-methyl-2,4-pentanediol, 1,2,6-hexanetriol and thioglycol. The humectant maybe employed in a concentration of from about 10 to about 50% by weight of the entire ink composition. In a preferred embodiment, diethylene glycol or a mixture of glycerol and diethylene glycol is employed a concentration of between 10 and 20% by weightof the entire ink composition.

The ink has physical properties compatible with a wide range of ejecting conditions, i.e., driving voltages and pulse widths for thermal ink jet printing devices, driving frequencies of the piezo element for either a drop-on-demand device or acontinuous device, and the shape and size of the nozzle.

A penetrant (0-10% by weight) may also be added to the ink composition employed in the process of the invention to help the ink penetrate the receiving substrate, especially when the substrate is a highly sized paper. A preferred penetrant forthe inks employed in the present invention is n-propanol at a final concentration of 1-6% by weight.

A biocide (0.01-1.0% by weight) may also be added to prevent unwanted microbial growth which may occur in the ink over time. A preferred biocide for the inks employed in the present invention is Proxel.RTM. GXL (Zeneca Colours Co.) at aconcentration of 0.05-0.5% by weight. Additional additives which may optionally be present in ink jet inks include thickeners, conductivity enhancing agents, anti-kogation agents, pH buffering agents, drying agents, and defoamers.

Ink jet inks made using polymers employed in this invention are employed in ink jet printing wherein liquid ink drops are applied in a controlled fashion to an ink receiving substrate, by ejecting ink droplets from plurality of nozzles, ororifices, in a print head of ink jet printers.

Commercially available ink jet printers use several different methods to control the deposition of the ink droplets. Such methods are generally of two types: continuous stream and drop-on-demand.

In drop-on-demand systems, a droplet of ink is ejected from an orifice directly to a position on the ink receiving layer by pressure created by, for example, a piezoelectric device, an acoustic device, or a thermal process controlled inaccordance digital data signals. An ink droplet is not generated and ejected through the orifices of the print head unless it is needed. Ink jet printing methods, and related printers, are commercially available and need not be described in detail.

To accelerate the printing speed and increase durability, an extra heating step can be added during the process of printing the ink composition of this invention. This heating step can be employed either during printing or after printing. In apreferred embodiment, heating is employed both during and after printing. Heating will help fluids to spread on a non-absorbing substrate as well as to accelerate its evaporation. Heating can also help ink components to penetrate into the non-absorbingsubstrate by swelling mechanism. The heating step during printing can be achieved using a heating means so that the non-absorbing substrate is heated to elevated temperature during the process of printing. The substrate is preferably heated to between30.degree. C. and 90.degree. C., more preferably between 40 to 70.degree. C. During the heating step after printing, the printed substrate is heated to elevated temperature using a heating means where substrate is heated to a temperature range between50.degree. C. and 150.degree. C., more preferably between 80 to 120.degree. C. Various methods may be used for the means of heating, for example, using light irradiation, a hot air source or an electrical heater. For the heating step during printing,an electrical heater or an infrared lamp is preferred. For the heating step after printing, light irradiation such as an infrared lamp is preferred. Optionally, an infrared absorbing material can be employed in the ink of the present invention toassist the heating by an infrared lamp.

The following examples illustrate the utility of the present invention.

EXAMPLES

Preparation of Pigment Dispersion

The magenta pigment dispersion contains: 300 g of Polymeric beads, mean diameter of 50 .mu.m (milling media); 30 g of quinacridone magenta pigment Pigment Red 122 (Sun Chemicals); 9 g of Oleoyl methyl taurine, (OMT) Potassium salt and 208 g ofDeionized water, and 0.2 g of Proxel GXL.RTM. (biocide from Zeneca). The above components were milled in a 2 liter double walled vessel obtained from BYK-Gardner using a high energy media mill manufactured by Morehouse-Cowles Hochmeyer. The mill wasrun for approximately 8 hours at room temperature. The dispersion was separated from the milling media by filtering the millgrind through a 4-8 .mu.m KIMAX.RTM. Buchner Funnel obtained from VWR Scientific Products. At the end of milling, additionalwater is added to the dispersion so that the pigment is about 10.0% by weight of the total final dispersion and the biocide is about 230 ppm by weight of the total final dispersion. The particle size is about 30 nm as measured by MICROTRAC II Ultrafineparticle analyzer (UPA) manufactured by Leeds & Northrup.

Preparation of Polymer Dispersions

Preparation of Comparative Polymer Dispersion 1 (PC-1: Acrylate)

600 g of deionized water and 3.6 g Triton 770.RTM. surfactant were charged to a 1-liter, three-neck round-bottom flask equipped with a mechanical stirrer and nitrogen inlet. The solution was purged with nitrogen for 30 min and heated to60.degree. C. in a constant temperature bath. 36.0 g of styrene, 90.0 g of butyl methacrylate and 54.0 g of methacrylic acid were added and stirred for three minutes. 16.4 g of 10% sodium persulfate solution and 5.5 g of 10% sodium metabisulfitesolution were added to initiate the polymerization. Polymerization was continued for one hour and heated one more hour at 60.degree. C. The temperature was reduced to 50.degree. C. and 1 ml each of t-butyl hydroperoxide (10%) and sodium formaldehydebisulfite (10%) were post-added. The content of the hydrophilic monomer is 30% by weight of the total polymer. The latex was cooled and filtered. The dispersion contains 22.2% solid by weight.

Preparation of Comparative Polymer Dispersion 1 (PC-2: Water Soluble)

Water soluble polymer Jonrez IJ-4655.RTM. is obtained from Westvaco as a styrene acrylic polymer solution at 25% Solids. The estimated content of the hydrophilic components in this polymer is about 40% by weight by titration.

Preparation of Polymer Dispersion 1 of the Invention (P-1)

160 g deionized water were charged to a 500 mL 1-neck round bottom flask equipped with mechanical stirrer. The flask was first flushed with nitrogen for 20 minutes, then immersed in a constant temperature bath at 40.degree. C. Afterwards, 0.25g of potassium persulfate, 0.35 g sodium metabisufite, 2.0 g Triton 770 (30% active), 4.0 g of ethyl acrylate, 36.0 g vinylidene chloride were added to the flask. The polymerization reaction was continued for additional 12 hours. The latex was cooledand filtered. The final polymer latex dispersion contained 13.52% solid by weight and the average particle size is 0.056 micron. This polymer contains no hydrophilic monomer. This polymer dispersion is designated as Polymer Dispersion 1 (P-1).

Preparation of Polymer Dispersion 2 of the Invention (P-2: Polyester)

Solid AQ-55.RTM. polyester ionomer was purchased from Eastman Chemical Company and then added to water with heat and agitation to obtain AQ-55 dispersion at 30% solids in concentration. The estimated content of the ionic hydrophilic monomer inthis polymer is less than 10% by weight. This polymer dispersion is designated as Polymer Dispersion 2 (P-2).

Polymer Dispersion 3 of the Invention (P-3: Polyurethane)

W-240.RTM. was a self-crosslinkable polyurethane purchased from Crompton Corporation as aqueous dispersion at 30% solids. The estimated weight percentage of the hydrophilic monomer in this polymer is less than 10% by titration. T his polymerdispersion is designated as Polymer Dispersion 3 (P-3).

Ink-2 of the present invention was prepared similar to Ink-1 except that 1.46 g of Polymer Dispersion 2 (30.0% active) was used instead of Polymer Dispersion 1 such that the final ink contained 2.2% of Polymer Dispersion 2 by weight of the totalink.

Ink 3 of the Invention (I-3)

Ink-4 of the present invention was prepared similar to Ink-1 except that 1.46 g of Polymer Dispersion 3 (30.0% active) was used instead of Polymer Dispersion 1 such that the final ink contained 2.2% of Polymer Dispersion 3 by weight of the totalink.

Comparative Ink 1 (C-1: Acrylic Latex With High Hydrophilic Content)

The comparative ink 1 was prepared similar to Ink-1 of the Invention except that 1.98 g of Comparative Polymer Dispersion PC-1 (22.2% active) was used instead of Polymer Dispersion 1. The final Ink contained 2.2% of Comparative PolymerDispersion PC-1.

Comparative Ink 2 (C-2: Water Soluble Polymer)

The comparative ink 2 was prepared similar to Comparative Ink 1 except that 1.76 g of Comparative Polymer Dispersion PC-2 (25% active) was used instead of Polymer Dispersion 1. The final Ink contained 2.2% of Comparative Polymer Dispersion PC-2.

Comparative Ink 3 (C-3: No Polymer)

The Comparative Ink 5 of the invention was prepared similar to Ink 1 of the invention except that 2.9 g of distilled water was used instead of Polymer Dispersion 1 so that the final ink did not contain any polymer latex.

Ink Firability Test

The inks of the present invention were filled into Epson 880 empty cartridges and printing was done with an Epson 880 Ink jet printer, using the above inks. All inks of the invention fired well through the Epson 880 printer, no nozzles wereclogged. The inks were left in printer for over 48 hours and the above printing test was repeated. All the nozzles were firing with minimum cleaning cycles without any problems for the inks of the present invention.

Ink Printing Reliability Test

The inks of the present invention were filled into an ink bag and tested using an Inkjet ink fixture apparatus having a Brother piezo printhead with a heatable printing drum. Ink drop volume was measured vs time to test the printing reliability. A 1" by 10" non-absorbing vinyl substrate, a multi-purpose inkjet cast vinyl (MPI 1005 #226 from Avery Graphics), was mounted on the printing drum. The drum was kept at 50.degree. C. during printing. A 0.7".times.4" Dmax density patch print target wasprinted. After printing, the samples were further heated at 90.degree. C. for 1 minute using an infrared lamp. A successful test result occurred when 20 pL ink droplets of the ink composition were continuously fired through the printhead at a rate of7,500 drops/second for at least an hour without nozzle failure or ink droplet misdirection.

Durability Test

Test Sample Preparation

A non-absorbing vinyl substrate, a multi-purpose inkjet cast vinyl (MPI 1005 #226 from Avery Graphics) was cut into 14 by 25 cm in size and placed on a heated coating block with temperature at about 40.degree. C. The above inks were filled intoan airbrush (Paasche Sirbrush Set H-3 available from Paasche Airbrush Company, Harwood Heights, Ill.) connected to compressed house air. The pressure of the airbrush was adjusted to about 20 lb such that smooth ink flow was obtained. The inks weresprayed onto the heated vinyl substrates described above. Uniform coatings of the inks were obtained. The selected samples were then heated at 90.degree. C. for 1 minute using an infrared lamp.

Dry Rub Resistance Test

The dry rub resistance test was carried out by rubbing the samples with a dry Q-tip for 4 passes under a consistent pressure in the inked area. The color loss in the treated sample area and the color transfer to Q-tip were examined visually anda rating of the dry rub resistance was given as follows on a scale of 0 to 5.

0: Best, No color loss, and/or color transfer;

1: hardly visible amount of color loss and/or color transfer;

2: visible amount of color loss and/or color transfer;

3: some color loss and color transfer;

4: large amount of color loss and color transfer;

5: Worst, almost complete color loss and color transfer.

Wet Rub Resistance Test

A wet rub resistance test was carried out by placing an approximately 2.54 cm diameter water droplet on the ink-coated sample surface for 5 minutes, after which the excess water was wiped off with a paper towel. The above treated area was thenrubbed with a dry paper towel for 4 passes under a consistent pressure a 3.5 cm diameter area. The color loss in the treated sample area and the color transfer to the paper towel were examined visually and a rating of the wet rub resistance was givensimilar as above on a scale of 0 to 5, 0 being the best and 5 being the worst. Both of the dry and wet rub resistance test results are shown in Table 1.

From the above table, it is evident that the presence of polymer latex in the ink significantly improves the image durability under both dry and wet conditions compared to the inks without polymer latex. The inks of the present invention showfarther advantages in image durability compared to the comparative inks.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.